The present invention relates to a method for making sputtering targets that reduces machine costs and improves quality and reliability, relative to conventional methods for preparing sputtering targets. The present invention further relates to methods of preparing improved metal discs. The present invention also relates to a method for reducing the manufacturing costs of sputtering targets and/or metal discs.
In the field of metal fabrication in general, and sputtering targets in particular, significant difficulties arise with regard to the costs associated with producing planar discs with very highly specific dimensional requirements. It is common practice in the field of manufacturing a metal disc to flatten both sides of a metal blank which is eventually formed into a metal disc, for example, a tantalum sputtering target preform. This requires the grinding of both sides of the metal blank, rolling both sides, or press flattening and/or surface conditioning of both sides of the metal.
Thus, for instance, a planar sputtering target preform can be machined from a rolled metal plate. Other methods of manufacturing sputtering target preforms, such as forging and subsequently processing of cylindrical metal billets, can be used. Typically, the dimensions of the sputtering target preform are larger than the dimensions of the resultant finished sputtering target blank after bonding onto a backing plate and finish machining operations are completed to produce a sputtering target assembly.
The manufacturing of a planar tantalum sputtering target involves the rolling of tantalum plate to a gauge that is typically 0.010-0.100 inches greater than the thickness of the finish machined target blank and a thickness tolerance of about 5-10% of the rolled gauge, level rolling to a nominal flatness of 0.050 inches, annealing the plate, rough cutting of blanks from the plate, several labor-intensive iterations of manual press flattening and surface conditioning to attain a flatness of 0.010 inches or less, and then machining the blanks to a desired diameter. These preform blanks are then sold to a sputtering target manufacturer, who bonds the blank to a backing plate, and then machines the face and diameter of the bonded preform to the dimensional requirements for the assembled sputtering target as specified by the sputtering equipment Original Equipment Manufacturer (OEM) or the target supplier's customers.
However, often the final metal disc or sputtering target produced is utilized in an application where, in fact, only one side of the disc or sputtering target truly benefits from and/or needs the highly specific dimensional properties.
Because of the high intrinsic cost and value of, for instance, tantalum, efforts are commonly taken to reduce the generation of scrap in the various manufacturing processes associated with tantalum. The target suppliers place tight dimensional tolerances on gauge and diameters of the blanks to minimize the weight of the material they purchase. Furthermore, the target suppliers would prefer blanks that meet a flatness of 0.005 inches, which would significantly improve the reliability of the bond between the target blank and the backing plate. However, achieving such stringent tolerances in gauge and flatness requires the grinding and the lapping of the blanks, a process which is prohibitively expensive and generates excessive amounts of low-value grinding scrap called swarf. Typically, the value of the tantalum contained in the swarf is less than the value of tantalum turnings generated by machining operations since it is often difficult and expensive to separate the tantalum particles from the grinding media comprising the swarf, and because of the greater propensity for contamination of the tantalum by grinding compared to machining.
Accordingly, there is a need to overcome one or more of the above described disadvantages.